The objective of this investigation is to elucidate the three dimensional structure of cytochrome c1 in the inner membrane of heart mitochondria and to describe the changes in structure which this protein manifests as it participates in oxidation-reduction reactions of the respiratory chain. Experiments will attempt to confirm the validity of an apparent non-heme containing subunit of the cytochrome and test the possible function of this subunit in electron transfer. Vesicles containing the cytochrome b-c1 complex of the inner mitochondrial membrane will be prepared and characterized in terms of size, enzyme content, and homogeneity of surface orientation. These vesicles will be used as a resolved membrane source in which to study cytochrome structure. Resolved membrane vesicles will be employed to measure the exposure of cytochrome c1 at the membrane surface, to identify which portion of the cytochrome interacts with adjacent electron carriers at the membrane interface, and to examine the latitude of motion of the heme-peptide region of cytochrome c1.